Geology topics

Gordon W. Tribble

Publications and source records attributed to Gordon W. Tribble.

3 recordsLinked to original sources

USGS1999

Ground-water resources in Kaloko-Honokohau National Historical Park, Island of Hawaii, and numerical simulation of the effects of ground-water withdrawals

Within the Kaloko-Honokohau National Historical Park, which was established in 1978, the ground-water flow system is composed of brackish water overlying saltwater. Ground-water levels measured in the Park range from about 1 to 2 feet above mean sea level, and fluctuate daily by about 0.5 to 1.5 feet in response to ocean tides. The brackish water is formed by mixing of seaward flowing fresh ground water with underlying saltwater from the ocean. The major source of fresh ground water is from subsurface flow originating from inland areas to the east of the Park. Ground-water recharge from the direct infiltration of precipitation within the Park area, which has land-surface altitudes less than 100 feet, is small because of low rainfall and high rates of evaporation. Brackish water flowing through the Park ultimately discharges to the fishponds in the Park or to the ocean. The ground water, fishponds, and anchialine ponds in the Park are hydrologically connected; thus, the water levels in the ponds mark the local position of the water table. Within the Park, ground water near the water table is brackish; measured chloride concentrations of water samples from three exploratory wells in the Park range from 2,610 to 5,910 milligrams per liter. Chromium and copper were detected in water samples from the three wells in the Park and one well upgradient of the Park at concentrations of 1 to 5 micrograms per liter. One semi-volatile organic compound, phenol, was detected in water samples from the three wells in the Park at concentrations between 4 and 10 micrograms per liter. A regional, two-dimensional (areal), freshwater-saltwater, sharp-interface ground-water flow model was used to simulate the effects of regional withdrawals on ground-water flow within the Park. For average 1978 withdrawal rates, the estimated rate of fresh ground-water discharge to the ocean within the Park is about 6.48 million gallons per day, or about 3 million gallons per day per mile of coastline. Although the coastal discharge within the Park is actually brackish water, the model assumes that freshwater and saltwater do not mix and therefore the model-calculated coastal discharge within the Park is in the form of freshwater discharge. Model results indicate that ground-water withdrawals in excess of average 1978 withdrawal rates will reduce the rate of freshwater coastal discharge within the Park. Withdrawals from wells directly upgradient of the Park had the greatest effect on the model-calculated freshwater coastal discharge within the Park, whereas withdrawals from wells south of Papa Bay had little effect on the freshwater discharge within the Park. For an increased ground-water withdrawal rate of 56.8 million gallons per day, relative to average 1978 withdrawal rates in the Kona area, model-calculated freshwater coastal discharge within the Park was reduced by about 47 percent.

Hawaii↗

USGS1997

Ground-water geochemistry of Kwajalein Island, Republic of the Marshall Islands, 1991

Ground water on Kwajalein Island is an important source of drinking water, particularly during periods of low rainfall. Fresh ground water is found as a thin lens underlain by saltwater. The concentration of dissolved ions increases with depth below the water table and proximity to the shoreline as high-salinity seawater mixes with fresh ground water. The maximum depth of the freshwater lens is 37 ft. Chloride is assumed to be non-reactive under the range of geochemical conditions on the atoll. The concentration of chloride thus is used as a conservative constituent to evaluate freshwater-saltwater mixing within the aquifer. Concentrations of sodium and for the most part, potassium and sulfate, also appear to be determined by conservative mixing between saltwater and rain. Concentrations of calcium, magnesium, and strontium are higher than expected from conservative mixing; these higher concentrations are a result of the dissolution of carbonate minerals. An excess in dissolved inorganic carbon results from carbonate-mineral dissolution and from the oxidation of organic matter in the aquifer; the stoichiometric difference between excess dissolved inorganic carbon and excess bivalent cations is used as a measure of the amount of organic-matter oxidation. Organic-matter oxidation also is indicated by the low concentration of dissolved oxygen, high concentrations of nutrients, and the presence of hydrogen sulfide in many of the water samples. Low levels of dissolved oxygen indicate oxic respiration, and sulfate reduction is indicated by hydrogen sulfide. The amount of dissolved inorganic carbon released during organic-matter oxidation is nearly equivalent to the amount of carbonate-mineral dissolution. Organic-matter oxidation and carbonate-mineral dissolution seem to be most active either in the unsaturated zone or near the top of the water table. The most plausible explanation is that high amounts of oxic respiration in the unsaturated zone generate carbon dioxide, which causes carbonate minerals to dissolve. Ground water contaminated by petroleum hydrocarbons had the highest levels of mineral dissolution and organic respiration (including sulfate reduction), indicating that bacteria are oxidizing the contaminants.

Kwajalein Island↗

USGS1993

Geohydrology and Possible Transport Routes of Polychlorinated Biphenyls in Haiku Valley, Oahu, Hawaii

A combination of geologic mapping, seepage runs, water-budget computation, analysis of stream-gaging records, study of stream sediment, and measurement of polychlorinated biphenyls (PCBs) was used to investigate the geohydrology and possible routes of PCB transport from areas of possible contamination in the U.S. Coast Guard's Omega Station in Haiku Valley, Oahu, Hawaii. The PCBs were a contaminant in fuel that was sprayed on vegetation and ignited during defoliation efforts at the Omega Station. Haiku Valley is a stream valley eroded into a thick section of dike-intruded, highly permeable lava flows. The valley is partly filled with alluvium, pyroclastics and massive lava flows. A shallow aquifer system is formed by a permeable unit of pyroclastics which is bounded below by less permeable alluvium, massive lava flows, and weathered basalt. A deeper aquifer system is present in the dike-intruded lava flows. Much of the area of suspected PCB-contaminated fuel application in Haiku Valley is situated on the geologic unit that forms the shallow aquifer. A water budget calculated for the drainage area of a stream-gaging station (16275000) at the downgradient boundary of the Omega Station indicates that the shallow and deep aquifers receive recharge of 5.1 cubic feet per second from the 0.98 square-mile drainage area; approximately 10 percent of the drainage area is suspected to have been contaminated by PCBs. Approximately 4 cubic feet per second of water is withdrawn from the aquifers by a well and a water tunnel in the valley, but the geology of the area indicates that some of the water withdrawn by the tunnel also comes from recharge beyond the surface-water divides of Haiku Valley. Base flow to the stream is about 1.2 cubic feet per second. A water-balance calculation between recharge, well and tunnel withdrawals, and stream base flow, indicates that 1.0 cubic feet per second or more of the water recharging the drainage area may travel through the subsurface and discharge downstream beyond the limits of the Omega Station. Mass-balance calculations indicate that the concentration of PCBs that dissolves in the ground-water as it infiltrates contaminated areas will be on the order of 10-7 micrograms per liter, but these calculations are based on a number of assumptions where data are lacking. Analysis of sediment from Heeia Stream indicates that the sediment is transporting PCBs past station 16275000. Although PCB concentrations in unfiltered stream water samples collected at the station were below detection limits 0.1 micrograms per liter, PCB concentrations ranged from 64 to 230 micrograms per kilogram in suspended sediment extracted from stream water. Because most of the suspended sediment in Heeia Stream is deposited in a wetland near the coast, the potential for PCB accumulation is greatest in the wetland.

Water-Resources Investigations Report↗